A device described in Japanese Patent Application Publication No. 2008-7094 (JP 2008-7094 A, Patent Document 1) is already known as an example of the control device that controls a vehicle drive device described above. Hereinafter, in the description in the “BACKGROUND ART” section, member names used in Patent Document 1 are cited in brackets for description. The control device [controllers 1, 2, 5, 7, 10, etc.] of Patent Document 1 is configured to be able to execute a plurality of travel modes by controlling the vehicle drive device. The plurality of travel modes include a WSC creep mode, a CL2 overheat mode, and a WSC active power generation mode.
In the WSC creep mode, the control device brings the first engagement device [first clutch CL1] into a direct engagement state and the second engagement device [second clutch CL2] into a slip engagement state, and a vehicle creeps with the torque of the internal combustion engine [engine E]. In the CL2 overheat mode, the control device controls both the first engagement device and the second engagement device into the slip engagement state, and the vehicle creeps with the torque of the internal combustion engine. In the WSC active power generation mode, the control device brings the first engagement device into the direct engagement state and the second engagement device into the slip engagement state, and the vehicle travels and the rotary electric machine [motor-generator MG] generates electric power with the torque of the internal combustion engine. The control device is able to execute mode transition between the WSC creep mode and the CL2 overheat mode and between the WSC creep mode and the WSC active power generation mode (refer to FIG. 6 of Patent Document 1, etc.).
The control device of Patent Document 1, during low-speed traveling in a state in which the amount of electric power stored in an electricity storage device [battery 4] is low, achieves the WSC active power generation mode in order to allow the rotary electric machine to generate electric power. However, in the WSC active power generation mode, only the second engagement device is in the slip engagement state; therefore, a state in which a differential rotational speed between engagement members on both sides of the second engagement device is large continues for a long period. This increases the amount of heat generation of the second engagement device, which may cause the second engagement device to get overheated. That is, it has been difficult to secure a desired amount of electric power while keeping the amount of heat generation of the second engagement device low in a specific traveling state such as low vehicle speed traveling.
On the other hand, in a state in which the vehicle speed has increased to a certain extent, the differential rotational speed between the engagement members on both sides of the second engagement device becomes comparatively small and the possibility of the second engagement device getting overheated becomes relatively low. Therefore, there are cases in which it is preferable to give priority to achieving other effects regarding vehicle traveling such as overall amount of heat generation of both of the engagement devices and the power generation efficiency of the rotary electric machine, or reducing shock to be transferred to the vehicle, etc. rather than only suppressing overheat in the second engagement device. In Patent Document 1, such matters are not particularly recognized.